1. Field of the Invention
This invention relates to a method of measuring optical characteristics of spectacle lenses and a lens meter in which it is possible to measure refraction characteristics of right and left lenses of a pair of spectacles individually by means of two measurement optical systems.
2. Description of the Related Art
A conventionally known lens meter includes: upper and lower accommodating protrusions provided on upper and lower portions of a front surface of a main body case and vertically spaced apart from each other; a lens rest provided on an upper surface of the lower accommodating protrusion; a lens table extending horizontally and mounted to the main body case so as to be movable forwards and backwards with respect to the lens rest; a nose pad support member mounted to the lens table so as to be horizontally and vertically movable; and a measurement optical system for measuring refraction characteristics of a lens placed on the lens rest. In this lens meter, the measurement optical system is equipped with an illumination optical system provided in the main body case and the upper accommodating protrusion and a light receiving optical system provided in the lower accommodating protrusion and the main body case.
Further, in this lens meter, the nose pads of a pair of spectacles are supported by the nose pad support member, and right and left lens rims of a spectacle frame are held in contact with a front surface of the lens table. In this state, the nose pad support member is moved horizontally and vertically, and the lens table is moved forwards and backwards to bring one of the right and left lenses into contact with the lens rest, measuring the refraction characteristics of that lens by the measurement optical system. To perform measurement on the other lens, the spectacle frame is moved in the same way as described above so as to bring the other lens into contact with the lens rest.
The above-described conventional lens meter has a problem in that, when performing measurement on the right and left spectacle lenses, it is necessary to bring the lenses one by one into contact with a single lens rest, which is a bother.
This problem might be solved by a lens meter equipped with a pair of optical systems for performing measurement on the right and left lenses of a pair of spectacles. In such a lens meter, to accurately measure the refraction characteristics of the spectacle lenses, it is necessary, in the measurement optical axis of each light receiving optical system, for the distance between the lower surface of the lens and the light receiving means of the light receiving optical system to be fixed. For this purpose, there has been proposed a construction in which a shaft-shaped lens rest is provided at some midpoint of the optical path of each of the right and left measurement optical systems to make the distance between the lower surface of the lens and the light receiving means of the light receiving optical system fixed.
Further, as an example of such a lens meter, there has also been proposed a construction in which optical characteristics of a spectacle lens at a multitude of points thereof are simultaneously measured by utilizing a measurement beam passing a periphery of a shaft-shaped (pin-shaped) lens rest, indicating refractive powers, etc. at the multitude of points as obtained from the measurement result through mapping display. In this case, in order to prevent displacement of the spectacle lens supported by the lens rest at the time of measurement, the spectacle lens is pressed against the lens rest by means of a lens presser.
However, since the spectacle lens is thus secured in position by means of this lens presser, it is impossible to project measurement beam to that portion of the spectacle lens where the lens presser exists, which that portion cannot be measured accurately.